1. Field of the Invention
The present invention relates to an optical transmission system including a plurality of optical transmission devices.
2. Description of the Related Art
Recently, regarding an optical transmission device, to achieve a high capacity of optical transmission, an optical transmission system operated by combining some basic optical transmission devices has been constructed. In such an optical transmission system constructed by combining a plurality of optical transmission devices (also called Shelves), when each optical transmission device is provided with information including a log-in ID for optical transmission device management, and when the information is managed for each optical transmission device, a system operation becomes complex. Accordingly, there is a strong demand for a system which enables an easier operation by managing an optical transmission system including a plurality of optical transmission devices as a single device, and reducing network resources.
FIG. 14 is a diagram showing a functional constitution in an optical transmission system (referred to as “conventional device”) which includes one basic optical transmission device. As shown in FIG. 14, the conventional device is arranged on a transmission line of optical signals. The conventional device includes a plurality of optical interface units (INF) 15 for receiving/transmitting optical signals from/to the other devices, and multiplexer/demultiplexer sections (referred to as MUX/DMUX sections, hereinafter) 12, 13 for multiplexing/demultiplexing the signals received by each of the interface units 15, and outputting to the interface units 15 corresponding to addresses of the signals. Each of the MUX/DMUX sections 12, 13 includes a signal connection converting section (cross connection) 12a for connecting an input signal to an outgoing path corresponding to its address.
Thus, two communication units (Units) which include the MUX/DMUX sections are disposed in the optical transmission device. One of the two MUX/DMUX sections 12, 13 is used as a working side (working line (WK)) device, and the other is used as a protection side (protection line (PT)) device used when the working side fails. Accordingly, the signal transmission line is made redundant. A state of the optical transmission device is monitored by a state monitoring section, and switching between the WK side and the PT side is carried out by a switching managing section.
There is a limit to the number of slots for connection to one basic optical transmission device, i.e., the number of optical interface units 15 mounted on one basic transmission device. Thus, to realize large-capacity transmission, an optical transmission system in which a plurality of basic optical transmission devices are interconnected must be constructed. To realize such a configuration, cooperation is necessary among the plurality of interconnected optical transmission devices in terms of signal connection. Accordingly, cooperation may conceivably be established among the optical transmission devices in terms of the signal connection by using parts of the optical interface units 15 to execute transfer of signals among the optical transmission devices.
However, when a capacity of the interface unit is used to connect each optical transmission device, a transmission permission amount of the device is consequently reduced by a connection amount with the other transmission device. Besides, presence of the signal connection converting section in each optical transmission device necessitates complex signal connection management.
Thus, in the configuration in which the plurality of optical transmission devices are connected, a functional constitution as shown in FIG. 15 is conceivable. FIG. 15 shows a functional constitution in the configuration in which the plurality of optical transmission devices are interconnected. According to the constitution, classification is employed in which one of the plurality of optical transmission devices becomes a main device (MAIN Shelf) 11, while the other optical transmission devices become expansion devices (Expansion (EXP) Shelves) 21. The signal connection converting section 12a is disposed in WK and PT MUX/DMUX sections 12, 13 alone mounted on the main device.
Accordingly, it is possible to concentrate management regarding complex signal connection conversion on the main device. Inter-optical transmission device connecting functions are provided to the WK and PT MUX/DMUX sections 12, 13 disposed in each optical transmission device, whereby signal connection conversion is enabled among the optical transmission devices, and information can be transferred between state monitoring sections 17a, 27a and between switching managing sections 171b, 271b of each optical transmission device.
According to the constitution, switching states (selecting states) of the WK/PT sides must be the same between the optical transmission devices. That is, when the WK MUX/DMUX section 12 is made active in the main device, the WK MUX/DMUX section 12 is similarly made active in the expansion device. Conversely, when the PT MUX/DMUX section 13 is used in the main device, the PT MUX/DMUX section 13 is similarly used in the expansion device. Otherwise, a signal phase difference is generated between the main device and the expansion device to cut off signals. Therefore, a switching operation of the communication unit which includes the MUX/DMUX sections 12, 13 must be executed in synchronization between the optical transmission devices.
Normally, the switching of the communication unit which includes the MUX/DMUX sections is controlled based on troubles of the unit such as a failure of the communication unit itself, unit omission, or a power supply trouble. However, in the functional constitution shown in FIG. 15, since the MUX/DMUX sections 12, 13 handle an optical line to transfer signals among the optical transmission devices, a trouble of the optical line must also be a cause of unit switching.
The signal to interconnect the optical transmission devices needs to have a signal capacity of about 100 gigabytes to realize a large capacity. Thus, many optical fibers are used to make connection. Accordingly, to set the trouble of the optical line as a cause of unit switching, line trouble states of the lines are collected by the optical transmission devices, and trouble information are combined for the entire system. A switching state that can save as many lines as possible must be determined from the huge amount of trouble information, and unit switching must be executed within a short time.
However, to manage a huge amount of trouble patterns and to decide a switching state which matches each trouble occurrence state, complex determination must be made, and much time must be expended for determination as to execution of switching. Accordingly, a case may occur in which standard switching regulations of 50 milliseconds by a single trouble and 100 milliseconds or less by a plurality of troubles cannot be met. A huge amount of test patterns must be implemented to test all the cases for the huge amount of trouble patterns, and much time must be expended to guarantee qualities. In addition, presence of the huge amount of trouble patterns makes difficult determination as to whether test patterns corresponding to all the trouble patterns are included or not, and establishment of a testing range. Therefore, it is difficult to secure a quality of the optical transmission system.
Note that conventional art documents concerning the present invention are as follows. The conventional art documents are “Japanese Patent Application No. 07-240732 A”, “Japanese Patent Application No. 2003-304274 A”, “Japanese Patent Application No. 03432958 B”, and “Japanese Patent Application No. 02570016 B”.